Method and a system for manufacturing a catheter and a catheter manufactured by that method

ABSTRACT

For manufacturing a catheter tubing ( 50 ), a container ( 1, 21 ) provided with a passage ( 15, 35, 36 ), a mandrel ( 7 ) sealing off that passage ( 15, 35, 36 ) when inserted into said passage and a solution ( 14 ) containing a dissolved plastic in the container ( 1, 21 ) up to a level above the passage ( 15, 35, 36 ) are provided. Repeatedly, the mandrel ( 7 ) is inserted into the passage and at least a section of the mandrel ( 7 ) is passed through the passage ( 15, 35, 36 ) and the solution ( 14 ) in an upward direction. When sufficient plastic material has adhered to the mandrel ( 7 ), the catheter tubing ( 50 ) is removed from the mandrel ( 7 ). Thus, catheters having thin, smooth walls of a uniform thickness can be manufactured without expensive machinery and tools. A system for carrying out the method and particular catheters obtainable by that method are also described.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method and a system for manufacturing acatheter and to a catheter manufactured by that method.

Known methods of manufacturing catheter tubing are extrusion anddipping. Advantages of the extrusion process are that it iswell-controlled and provides a catheter tubing with a smooth thin wallof a very constant thickness. However, extrusion requires relativelyexpensive machinery end tools. Therefore, it is mainly suitable for theproduction of substantial lengths of catheter tubing having a uniformcross-section, To manufacture a catheter, the catheter tubing has to becut to the required length(s) and fittings have to be connected to thetubing. To avoid blood damage when the catheter is brought in contactwith a pationt's blood in-vivo, special adhesives have to be used andsmooth transitions at the fittings are required. Furthermore, cathetersgenerally comprise reinforcement material which is uncovered when thecatheter is cut to the required length. Special measures are required tocover the reinforcement material to avoid contact between a patient'sblood and the reinforcement material.

In UK patent application 2 187 670 it is described to manufacture acatheter having a funnel portion of rubber or other suitable material byplacing the funnel over a former and dipping the catheter with theformer one or more times in a latex solution.

However, dipping has been found difficult to control and did not providesatisfactory results, as is described in “Transarterial Blood Pumps,Feasibility Phase, Final Report”; Authors: H. Duffor at al.; Ed.: Dr OrG. J. Verkerke and Dr G. Rakhorst—Groningen ISBN 90-74280-02-1.

Furthermore, a particular requirement of catheters to be brought indirect contact with a patient's blood is that the ends and transitionsat fittings are as smooth as possible and that all surfaces to becontacted with blood consist exclusively of biocompatible materialswhich cause as little damage as possible to the blood.

SUMMARY OF THE INVENTION

One object of the invention is to provide a method of manufacturing acatheter efficiently on a small scale without expensive machinery ortools, so that catheters can efficiently be manufactured in a greatvariety, and with which catheters with smooth, thin walls of uniformthickness can be obtained.

Another object of the invention is to provide a low-cost system withwhich catheters can be manufactured efficiently at small scale in agreat variety of lengths and shapes, and with which catheters withsmooth, thin walls of uniform thickness can be manufactured.

Yet another object of the invention is to provide catheters which areparticularly smooth at the ends or in the area of fittings to reduceblood damage to a minimum.

According to the present invention, catheters having smooth thin wallsof constant thickness can efficiently be manufactured on a small scalewithout expensive machinery or tooling by a method in which use is madeof a container with at least one passage in a lower part thereof, amandrel sealing off this passage when inserted therein and a solutioncontaining a plastic in the container, a cycle of inserting the mandrelinto the passage and moving at least a section of the mandrel throughthe passage and the solution in an upward direction is repeatedlycarried out to form a catheter tubing on said section of the mandrel,and the catheter tubing formed on the mandrel is removed from themandrel.

As in a dipping method, the thickness and the distribution of theplastic material over the mandrel depends on the viscosity of thesolution, the gravity and the velocity at which the mandrel is pulledout of the solution. However, since consecutive sections of the mandrelenter the solution from below and leave the solution in upwarddirection, a uniform residence time in the solution of at least asubstantial part of the mandrel during each cycle can easily be obtainedby passing that part of the mandrel through the solution with a constantvelocity. Thus, the extent to which plastic adhered to the mandrel isaffected by the solvent during immersion in the solution is uniformlydistributed over the part of the mandrel passed through the solution ata constant velocity. This results in a well-controlled uniform thicknessof each layer. A multitude of these layers applied consecutively forms acatheter tubing constituted by a plurality of very thin layers andhaving a uniform thickness. Since the mandrel may be held vertically, noparticular measures for avoiding bending of the mandrel are required.

If a predetermined variation of the residence time over the length ofthe mandrel is desired, the velocity of the mandrel can be variedaccordingly.

In accordance with a further aspect of the invention, a systemspecifically adapted for carrying out the method according to theinvention is provided, which system includes a container with a cavityfor holding a solution containing a dissolved plastic material, whichcontainer is provided with at least one passage in a lower part of thecavity, a mandrel sealing off that passage when inserted into thatpassage, and means for passing at least a section of said mandrelthrough said passage in an upward direction.

The invention can further be embodied in a catheter which canspecifically be obtained by a particular mode of carrying out the methodaccording to the invention. Such a catheter according to the presentinvention includes a tubing and a fitting, the fitting beingencapsulated by wall material of the tubing extending along the insideand the outside of said fitting.

Such a catheter can for example be manufactured by positioning thefitting over a wall coating previously applied to the mandrel and bysubsequently applying the further layer or layers of wall material.

When the catheter is finished, a continuation of the wall material ofthe tubing of the catheter encapsulates at least parts of the fitting,so that a very smooth seamless outer surface is obtained in the area ofthe fitting. Any adhesive between the wall material and the fitting isshielded from blood and tissue of the patient, when the catheter extendsinto a patient.

Further details and advantages of the method, the system and thecatheter according to the present invention appear from the followingdescription, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system according to theinvention for carrying out the method according to the invention;

FIG. 2 is a side view in cross section of a container for use in thesystem shown in FIG. 1;

FIG. 3 is a graph showing a wall thickness distribution obtained withthe method according to the invention;

FIG. 4 is a side view in cross section of a second container for use inthe system shown in FIG. 1 along the plane IV—IV in FIGS. 5 and 6;

FIG. 5 is a top plan view in cross section along the line V—V in FIG. 4;

FIG. 6 is a top plan view in cross section along the line VI—VI in FIG.4;

FIG. 7 is a schematic side view in cross section of a part of a cathetercomprising a fitting positioned over a mandrel;

FIG. 8 is a side view of a catheter according to the invention;

FIG. 9 is a schematic side view in cross section of a part of a catheteraccording to the invention comprising a fitting positioned over amandrel; and

FIG. 10 is a side view of the fitting of the catheter shown in FIG. 9.

MODES FOR CARRYING OUT THE INVENTION

In FIG. 1 a system according a presently most preferred embodiment ofthe invention for manufacturing a catheter is schematically shown.

The system is composed of a container or receptacle 1, 21, a liftingassembly 2 arranged above that container 1, 21 and a mandrel 7. Thelifting assembly consists of a motor 3, a gear box 4, a spool 5 and acord or string 6 from which the mandrel is detachably suspended.

To position the container 1, 21 and the lifting assembly 2 in thedesired configuration, the container 1, 21 and the lifting assembly 2are mounted on a support structure 8, composed of a vertical column 9, afoot 10 and an arm 11 whose position along the column 9 is adjustable.The arm 11 is provided with a clamp 12 for holding the container 1, 21.

Containers 1, 21 for use in the system shown in FIG. 1 are shown in moredetail in FIGS. 2, 4, 5 and 6. The containers 1, 21 are provided with acavity 13, 33 for holding a solution 14, 34 containing a dissolvedplastic material. Furthermore, the containers 1, 21 are each providedwith at least one passage 15, 35, 36 spaced from the top of the cavity13, 33. Preferably, the passages 15, 35, 36 are provided in the bottomof the containers 1, 21 to allow passage of the mandrel 7 therethroughin a vertical direction.

The mandrel 7 and the opening 15 or openings 35, 36 have cross-sectionsadapted to allow passage of the mandrel 7 through the passage 15 orpassages 35, 36 and to ideal off the passage 15 or passages 35, 36 whilethe mandrel 7 extends therethrough.

By the lifting assembly 2, the mandrel 7 or at least a section of themandrel 7 can be passed in upward direction through the passage 15 orpassages 35, 36.

Manufacturing a catheter tubing using the system shown in FIG. 1 withthe container shown in FIG. 2 is started by inserting the mandrel 7 intothe opening 15 so that the opening 15 is sealed and connecting themandrel 7 to the cord 6 of the lifting assembly 2. Then the solution 14containing a dissolved plastic is fed into the container 1 up to a levelabove the passage 15. Then, a section of the mandrel 7 is moved throughthe passage 15 and the solution 14 in an upward direction by energizingthe motor 3.

The mandrel 7 can be lifted until it leaves the opening 15. The solutionflowing away through the opening can be caught in a receptacle providedunder the opening. It is also possible to remove the solution 14 justbefore the mandrel 7 is pulled out of the opening 15. A thirdpossibility is to provide at least one plug 43 or other mandrel (seeFIG. 2) of essentially the same cross section as the mandrel 7 andadapted to be in sealing contact with, alternately, the leading and thetrailing end of a mandrel 7. Such a plug or other mandrel seals off theopening when the mandrel 7 has passed the opening until the nextmandrel, yet another mandrel or again the same mandrel 7 is insertedinto the opening 15. Thus, the solution 14 can also be held in thecavity 13 after the mandrel 7 has left the opening 15. The solution onlyhas to be replenished to replace solution which has adhered to themandrel or mandrels. Some additional solvent may have to be replenishedto replace evaporated solvent.

The plug 43 is provided with a projection 44 at its leading end and arecess 45 at is trailing end to allow concentric positioning withleading and trailing mandrels 7. Sealing rings 46, 47 at both thetrailing and leading ends of the plug 43 are provided to avoid leakingbetween the plug and leading or trailing mandrels 7.

The steps of pulling the mandrel 7 through the opening 15 and thesolution 14 and, if necessary, collecting solution drained through theopening 15 and refilling the cavity 13 each time the opening 15 isclosed upon a next passage of the mandrel 7, are repeated until thelayer of catheter tubing wall material adhered to the mandrel 7 has therequired thickness.

To provide the solution in the container at the beginning of eachdrawing cycle, the mandrel 7 may each time be inserted into the passage15 before the solution 14 is fed to the cavity 13.

However, if the passage is closed off between successive passages of themandrel 7, e.g. by a plug or another mandrel as described above, it isnot necessary to fend the solution 14 into the cavity 13 each time themandrel 7 has ben inserted into the passage, because the solution 14 isalways held in the cavity 13.

Draining of the solution via the passage 15 can also be avoided byproviding a flap-shaped valve which closes off the passage 15 when nomandrel extends through the passage. Another possibility of avoidingdraining of the solution via the passage 15 is to drain the solution viaa draining channel communicating with the interior of the container justbefore the trailing end of each mandrel leaves the passage 15. Thedraining channel or another channel can be used for refilling thecontainer each time a leading end of a mandrel has been inserted intothe passage 15. The container can also be refilled by simply pouring thesolution into the container from above.

Finally, the catheter tubing wall material adhered to the mandrel can beremoved from the mandrel 7.

FIG. 3 shows that a very even thickness distribution can be obtained.The results shown in FIG. 3 were obtained under the followingconditions:

Mandrel: PTFE 400×8 mm

Drawing volocity: 3 mm/s

Concentration: 10%

Plastic: polyetherurethane (Pellethane 80 AE made by Dow)

Solvent: tetrahydrofuran

Number of draws: 6

Time between successive draws: 5 minutes

Temperature: room temperature

These results proved to be very well reproducible. The surface wassmooth. No drops or air bubbles appeared in the adhered plastic. Thecatheter wall tubing formed around the mandrel was easily removable fromthe PTFE mandrel. In spite of the vertical orientation of the mandrel,the wall thickness showed no increase towards one end of the catheterdue to wall material descending along the mandrel.

To easily accommodate the cross section of the opening to the increasingtotal thickness of the mandrel and the wall material adhered to thomandrel 7, the passage 15 and the passages 35, 36 each have flexibleedges 17, 37. In the preferred embodiment, this is achieved by providingthe passages 15, 35, 36 in the form of holes in flexible (preferablylatex) membranes 1 a, 38. The membranes 18, 38 can be fixed by aclamping ring 19 extending around a container body 20 as is shown inPig. 2. The size of the passage 15 is slightly smaller than the size ofthe mandrel and the form of the passage 15 corresponds to the form ofthe cross section of the mandrel 7 (in the present embodiment both havea circular shape). When the mandrel 7 is inserted into the passage 15,the edges of the passage 15 are slightly stretched so that the size ofthe passage 15 is increased to the size of the cross section of themandrel 7 and any material applied to the mandrel 7.

In particular for large lumen catheters it is on the one hand desirableto have a wall which is as thin as possible to obtain a great innerlumen at an outer diameter which is as small as possible, while, on theother hand, the catheter must be able to withstand substantialover-pressure (generally at least about 95 kPa) and under-pressure(generally at least 60 kPa), To prevent the catheter from expanding orcollapsing a reinforcement can be applied around the plastic layeradhered to the mandrel 7. Depending upon the required properties of thecatheter, the reinforcement may for example be made of stainless steelwire, nylon or special high-modulus fibres such as carbon fibre oraramide embedded in epoxy resin. The material can for example be appliedaround the plastic layer adhered to the mandrel 7 in the form of asingle or repeated spring, successive rings, a weave, a braid orlongitudinal bars. The catheter 40 shown in FIGS. 7 and 8 is providedwith a single coil 41 of stainless steel wire of a diameter of 0.12 mmwith 2.4 windings per mm and showed both a good flexibility and therequired resistance against over-pressure and under-pressure. Moreover,the reinforced catheter tubing proved easy to cut to the requiredlength, because only one wire has to be cut.

To avoid direct contact between the reinforcement 41 and the patient'sblood and to provide a smooth outer surface, the reinforcement has to becovered with an outer coat.

According to the preferred mode of carrying out the method according tothe invention, a container having two passages 35, 36, as shown in FIG.4, is provided and an interspace 39 between these passages 35, 36 isalso filled with the solution 14.

To this and the system is provided with a container 21 as shown in FIGS.4, 5 and 6 having two passages 35, 36 in an axially spaced configurationand a chamber 39 between these passages 35, 36.

When the mandrel 7 is passed through the two passages 35, 36, the edgesof the lower passage 36 essentially prevent fluid from leaking downalong the mandrel 7. The edges of the upper passage 35 rake bubbles fromthe passing mandrel 7. In this manner, smooth, substantially bubble freefurther layers are obtained. A particular advantage of providing two ormore of the passages 35, 36 is that leaking and entraining of bubblescan effectively be counteracted at a low contact pressure between theedges of the passages and the material passing through the passage, sothat relative displacements of the windings of the reinforcements by theedges of the passages can be avoided. Such displacements would lead toan uneven distribution of the pitch between successive windings and thusa stiffness which varies along the length of the catheter.

To assure that the chamber 39 between the passages remains filled withsolution, the cavity 33 of the container communicates with the chamber39 via accommodating passages 42. In the present embodiment, theseaccommodating passages are provided in the form of holes 42 in the uppermembrane 38.

Although the container according to FIGS. 4, 5 and 6 is particularlyadvantageous for applying material to an uneven basis, for example afterreinforcements or fitting have been applied to the mandrel, it can ofcourse also be used to apply plastic material to an even basis, such asdirectly to the mandrel. The same containers can thus be used forapplying the plastic material before and after reinforcements have beenapplied.

The material encapsulating the reinforcement can advantageously beapplied under the same conditions as described above with respect to thelayers applied before the reinforcement was applied, except thatpreferably a container as shown in FIGS. 4, 5 and 6 is used.Particularly good results have been obtained with the use of apolyesterurethane (Estane 74 D from B.F. Goodrich). This material issomewhat stiffer than Pellethane 80 AE, which may also be advantageousfor the layers applied before the reinforcement is applied.

A particular advantage of the system and the method according to thepresent invention is that catheters with a great variety of integratedfittings can efficiently be manufactured. Moreover, the catheters caneven be tailor-made with fittings exactly in positions specified forparticular patients and clinical applications.

According to the preferred mode, first an inner coat is applied to themandrel 7, whereafter the inner coat is cut to sections of the requiredlengths. Some sections of inner coat are removed from the mandrel 7.Then fittings 48, 49 and removed sections of inner coat are positionedonto the mandrel, cone shaped sockets 52 of the fittings 48, 49 areurged under ends of the inner coat sections and preferably bonded to theinner coat ends by an adhesive. Then the reinforcement is applied overthe inner coat and the fittings 48, 49, a wider pitch between successivewindings being formed where the windings extend directly along theoutside of the fittings 48, 49. Finally, the assembly thus obtained isagain drawn through the solution 14 as described again until therequired outer coat encapsulating the reinforcement and at least partsof the fittings 48, 49 has been obtained.

The fitting 48 is provided with a helical groove 53 receiving a windingof the reinforcement extending along the outside of a central part ofthe fitting 48, so that the helical projecting edge formed by thiswinding is avoided, or at least reduced in size, and additional axialfixation of the fitting 48 is obtained.

By positioning the fittings 48, 49 over the mandrel 7 between two of thecycles in each of which cycles the mandrel 7 is drawn through thesolution 14, a catheter 40 with fittings 48, 49 completely or partiallyencapsulated by wall material of the tubing 50 of the catheter isobtained. More specifically, the seam between wall material appliedbefore the fitting was mounted and material of the fitting is alsoencapsulated by wall material of the cathoter tubing. This results in avery smooth outer surface. Furthermore, any adhesive in the seam isencapsulatod by wall material and thus shielded from blood and tissue ofthe patient when the catheter is in use extending into a patient.

Thus, for example a catheter 40 as shown in FIGS. 7 and 8 can beobtained which catheter 40 comprises a tubing 50 and a fitting 48encapsulated by wall material 51 of the tubing 50. The wall material 51encapsulating the fitting 48 has a stepped thickness at the ends of theparts of wall material applied to the mandrel 7 before the fitting 48was positioned onto the mandrel 7, as a result of which the step at theproximal end of each socket is smoothed.

By applying the reinforcement 41 after the fittings 48, 49 have beenpositioned onto the mandrel 7, the reinforcement also extends aroundparts of the fittings 48, 49. The reinforcement wound around the fittingprovides a particularly reliable integration of the fittings 48, 49 inthe catheter 40.

At the fitting 48, which is positioned between ends of the catheter 40,the wall material 51 of the tubing 50 enveloping the fitting 48 forms acontinuation in longitudinal direction of wall material of the tubing50, bridging wall material of the tubing on one side of the fitting 48and wall material of the tubing at the opposite side of the fitting 48.Thus, the outer coat only has to be interrupted at the fitting 49 wherethis is required for providing a passage to the inside of the fitting48. The fitting 48 may for example be provided in the form of a valvestructure.

To de-aerate the catheter 40, the catheter has to be closed off outsidethe patient's body. To this end, the distal end (the end opposite thefitting 49) of the catheter 40 is provided with a connector 54. Theconnector 54 is attached to the catheter tubing 50 without forming anarrowed inside cross section and may for example be connected to aconnector of a heart pump.

In FIG. 9 a section of a catheter 60 is shown which is manufactured in aslightly different manner. The fitting 58 is positioned over plasticmaterial applied to the mandrel 7 during previous passages of themandrel 7 through the solution 14. Then the reinforcement is appliedover the inner coat and the fittings as in the example describedhereinbefore. In this example the pitch of the windings 41 of the coilis maintained the same where the windings are wound around sockets 62 ofthe fitting 58. A wider pitch is provided where the windings extendalong a central part of the fitting 58 to obtain an interspacesufficiently large for a passage interconnecting the inside and theoutside of the catheter 60. Finally, as in the example describedhereinbefore, the assembly thus obtained is again drawn through thesolution 14 until the required outer coat encapsulating thereinforcement and at least parts of the fitting 58 has been formed.

By positioning the fitting 58 over plastic layers applied to the mandrel7 during previous passages of the mandrel 7 through the solution 14 andby passing the mandrel 7 through the solution 14 after the fitting 58has been positioned onto the mandrel 7, a catheter 60 with a fittings 58completely or partially encapsulated by wall material of the tubing 50of the catheter on its inside and its outside is obtained. The catheter60 has no seams between wall material of the tubing 50 and material ofthe fitting 58. Instead, the fitting 58 is encapsulated by continuouslayers of wall material of the catheter tubing. This results in a verysmooth inner and outer surface. because the fitting is encapsulatedbetween continuous inner and outer layers of wall material of the tubing50, the integrity of the catheter is substantially improved. Especiallythe resistance against delamination between the fitting 58 and wallmaterial of the tubing 50 when a portion of the catheter 60 adjacent thefitting 58 is bent sharply is substantially increased.

Fittings for a catheter often comprise a passage allowing communicationbetween the inside of the catheter and the outside of the catheter. Toprovide passages through wall material of the catheter after the fitting58 has been positioned and the formation of wall material has beencompleted, the wall material can be cut away where the passages arerequired.

As appears from FIG. 10, the fitting 58 is provided with a centralopening 61 into which a valve-unit can be mounted.

The sockets 62 of the fitting 58 are provided with openings 63. Whenplastic material is applied after the fitting 58 has been brought inposition, plastic material fills up the openings and forms anchorsbetween plastic material on the inside and the outside of the sockets62. Thus the structural integrity between the fitting 58 and the wallmaterial of the tubing 50 is further increased. Dependent on the designof the sockets and the plastic material used, the openings 63 can alsobe of a different design and be provided in different patterns.

What is claimed is:
 1. A method of manufacturing a catheter (40)comprising the steps of: providing a container (1, 21) provided with atleast one passage (15, 35, 36); providing a mandrel (7) sealing off saidpassage or passages (15, 35, 36) when inserted into said passage orpassages (15, 35, 36); providing a solution (14) containing a dissolvedplastic in said container (1, 21) up to a level above said passage orpassages (15, 35, 36); forming a catheter tubing on the mandrel (7) byrepeatedly carrying out a cycle of: a. inserting said mandrel (7) intosaid passage or passages (15, 35, 36); and b. moving at least a sectionof said mandrel (7) through said passage or passages (15, 35, 36) andsaid solution (14) in an upward direction; and removing the cathetertubing (50) formed on said mandrel (7) from said mandrel (7).
 2. Amethod according to claim 1, wherein at least two of said passages (35,36) are provided and ai interspace (39) between said passages (35, 36)is filled with said solution (14).
 3. A method according to claim 1,wherein between two of said cycles a fitting (48, 49, 58) is positionedonto said mandrel (7).
 4. A method according to claim 3, wherein acone-shaped socket of the fitting (48, 49) is urged in-between a sectionof the mandrel (7) and plastic material applied to that section of themandrel (7) during previous passages of that section through thesolution (14).
 5. A method according to claim 3, wherein the fitting(58) is positioned over plastic material applied to that section of themandrel (7) during previous passages of that section through thesolution (14).
 6. A method according to claim 3, wherein, between two ofsaid cycles, a reinforcement (41) is applied to layers formed on themandrel (7) after the fitting (48, 49, 58) has been positioned onto saidmandrel (7).